Preparation of shape memory polyurethane composite materials by grafting PCL onto CNFs with different carboxyl content

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Abstract This paper presented the preparation of cellulose nanofiber (CNFs) with different amount of carboxyl groups from rice straw pulp using TEMPO/NaBr/NaClO oxidation system. It is found that the obtained CNFs were in nano fibers with an average diameter of 6 nm and an average length of 160 nm. Subsequently, the CNFs were grafted with polycaprolactone (PCL) to form the grafted product CNFs-g-PCL, which was blended with shape memory polyurethane (SMPU) to obtain CNFs-g-PCL/SMPU composites. The graft ratio of PCL on CNFs decreased from 24.6–10.7% as the carboxyl content in CNFs increased 0.35mmol/g to 1.14mmol/g. So the hydrophobicity of the grafted product (CNFs-g-PCL) also decreases as the carboxyl content increases in CNFs. When the addition of CNFs-g-PCL was 10%, the elastic modulus (up to 54.4%) and tensile stress (up to 67.3%) of the CNFs-g-PCL / SMPU composite were both higher than those of the pure SMPU. In addition, the shape retention and shape recovery rates of the composite did not significantly change after the addition of CNFs-g-PCL. Therefore, the addition of CNFs-g-PCL can improve the mechanical properties of SMPU while maintaining its shape memory properties.

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